A half-smoked cigar, abandoned by wartime prime minister Winston Churchill, is up for sale in Norfolk.

The four-inch unfinished "smoke" could fetch more than £300 because it came from the lips of the famous cigar-smoking statesman before he dashed away to an urgent cabinet meeting.

Proof of its owner is thanks to an enterprising Downing Street valet, Nellie Goble, who grabbed the cigar, and a sheet of number 10 notepaper, on which she penned a note to a friend saying: "Just a small souvenir to remind you at some future date of one of the greatest men that ever lived in England."

The cigar will be sold on Friday, January 29, at Keys auction room at Aylsham, where expert Andrew Bullock expected it to excite worldwide interest among collectors of Sir Winston Churchill memorabilia.

Cigars belonging to Churchill occasionally came up for sale, but "I am not aware of many others that have survived after being half-smoked by the great man himself," he said.

"It was extremely rare for Churchill not to finish a cigar, so it must have been something very, very urgent that demanded his immediate attention in the cabinet room. As this was wartime, it is fascinating to speculate as to what it might have been that was so important," said Mr Bullock.

It was on August 22, 1941, that the cigar was abandoned - a day when the advancing German army reached Leningrad, leading to a historic siege.

And just a week earlier, Churchill had been in top secret meetings with American president Franklyn D Roosevelt, on board a cruiser anchored off Newfoundland, over the Atlantic Charter, a blueprint for a post-war world, which was the seed for the creation of the United Nations.

The call that interrupted his cigar could have related to either of those momentous happenings.

The cigar was treasured by Nellie's friends and proudly shown off to visitors, then passed to a daughter, now a pensioner living in north Norfolk who kept the stub wrapped in the precious note in a drawer.

She wanted to remain anonymous but said: "It rarely comes out of the drawer, so it seems better to sell it to someone who will truly appreciate it. If it doesn't fetch the earth, it won't break my heart. I just want it to go to somebody who will get some real pleasure from owning it."

In November, a butter dish used as an ashtray by Churchill at the London dining and debating club he co-founded was sold for £4,200 - almost three times its estimate.